In detergent applications, large volumes of chemicals are used. Because these chemicals may eventually enter the environment and reside in subsurface waters or open bodies of surface waters, it is highly desirable for such chemicals to be degradable in order to reduce any environmental problems.
Traditionally, detergents and cleaning agents have contained phosphates. These phosphates are added as detergent builders, to sequester alkaline earth metal hardness ions, as incrustation inhibitors and as anti-redeposition agents. Despite the fact that the well known inorganic phosphorus compounds are highly effective and relatively non-toxic, they lead to environmental problems by causing excess plant growth, resulting in eutrophication of lakes.
During the past three decades, efforts have been made in the detergent industry to convert from the eutrophying phosphates to more environmentally acceptable materials such as polycarboxylic acid polymers and copolymers. Examples of such polycarboxylic acid polymers and copolymers are polyacrylic acid and acrylic acid and maleic acid copolymers.
While the polycarboxylic acid polymers and copolymers currently used in detergent and water treatment applications do not suffer from the same drawbacks as the phosphorus-containing inorganic builders, it is desirable that such chemicals used in large volume applications which enter the environment be biodegradable. Unfortunately, most polycarboxylic acid polymers and copolymers useful in detergent applications or as dispersants or as water treatment chemicals are not highly biodegradable. However, the present invention solves this problem by producing terpolymers having improved biodegradation properties relative to homopolymers or copolymers of polycarboxylic acids.
Most polymers used in detergent applications are polymerized via aqueous polymerization processes which have several drawbacks. First, in an aqueous process, the amount of each monomer that can be incorporated into the final terpolymer is limited by the solubility of the monomer in water. Therefore, the amount of a desirable monomer that can be incorporated into the final product is limited. Second, hydrolyzable functional groups present during the aqueous polymerization process will be hydrolyzed during the polymerization and may lead to an undesirable product. For example, if vinyl acetate is used in an aqueous process, it is partially converted to undesirable acetaldehyde. The present invention avoids these problems associated with an aqueous process by polymerizing terpolymers in a non-aqueous solvent.
U.S. Pat. No. 3,268,491 discloses an aqueous process for the preparation of vinyl acetate and dicarboxylic acid copolymers. Specifically, this process tries to prevent the hydrolysis of the vinyl acetate by requiring the presence of a redox catalyst in an amount of from 3 to 15 percent by weight, based on the total weight of the monomers, and strictly controlling the pH between 3 and 6. This process only discloses the use of vinyl acetate and dicarboxylic acid monomers to form copolymers, and does not disclose the possibility of using other monomers to form terpolymers.
U.S. Pat. No. 3,887,480 improves on the process disclosed in U.S. Pat. No. 3,268,491, discussed above, and discloses an aqueous process for preparing water-soluble polymers of maleic acid with at least one other copolymerizable monomer. This process requires the carrying out of the reaction in the presence of an amount not less than 17 percent by weight based on the sum of the monomers, of a persulfate catalyst. Despite the improvement over the previously discussed patent, this process has several problems. The very high catalyst content adds additional cost to the process, consumes additional chemicals and, because of the availability of additional peroxo groups, significantly changes the composition of the copolymers.
Canadian Patent No. 1,243,446 discloses another aqueous process for the preparation of copolymers containing from 10 to 60 percent by weight of the total monomer content of a monoethylenically unsaturated dicarboxylic acid, 40 to 90 percent by weight of a monoethylenically unsaturated monocarboxylic acid and from 0 to 20 percent by weight of a monomer free from carboxyl groups. This aqueous process requires from 0.5 to 5 percent hydrogen peroxide by weight, based on the monomers.
U.S. Pat. No. 4,659,793 discloses an aqueous process for the synthesis of copolymers of monoethylenically unsaturated dicarboxylic acids, such as maleic acid, with monomers selected from the group consisting of (a) monocarboxylic acids, such as acrylic acid, (b) an organic sulfonic acid compound, such as 2-acrylamido-2-methylpropanesulfonic acid, (c) a carboxyl-free monomer, such as vinyl acetate, and mixtures of said monomers (a), (b) and (c). This patent discloses an improved polymerization for the manufacture of these water-soluble polymers by using low levels of metal ions to promote copolymerization and reduce the amount of residual monomer. The amount of monomer (c), the carboxyl-free monomer, is dependent on the solubility of monomer (c) and is not greater than 30 percent of the total monomer employed.
Copending U.S. patent application Ser. No. 502,100 ('100) filed on Mar. 30, 1990, commonly assigned to the same assignee as the present invention, also describes a method of preparation of copolymers of monoethylenically unsaturated aliphatic dicarboxylic acids with .alpha.,.beta.-ethylenically unsaturated monomers. The '100 application describes an aqueous polymerization process for producing copolymers of more consistent composition by the simultaneous addition of the monomers to the reaction vessel. Again, as disclosed in U.S. Pat. No. 4,659,793, a carboxyl-free monomer can be used, but again, the concentration of the carboxyl-free monomer is dependent on its solubility. Furthermore, the carboxyl-free monomer could be susceptible to hydrolysis during the aqueous procedure.
In the publication, Copolymers of Acrylic Acid with Vinyl Alcohol, Methyl Vinyl Ether and 2-Hydroxy-Acrylic Acid, Yukagaku, 34(6) 456 (1985), a copolymer of sodium acrylate and vinyl alcohol, and a copolymer of disodium maleate and vinyl alcohol were reported for use as a detergent builder. The copolymer of sodium acrylate and vinyl alcohol was prepared by an aqueous polymerization of acrylic acid and vinyl acetate followed by neutralization with a 20 percent solution of sodium hydroxide to form the sodium acrylate and vinyl alcohol copolymer. Only copolymers containing from 3 to 12 mole percent vinyl alcohol were prepared. The copolymer of disodium maleate and vinyl alcohol was prepared by an aqueous polymerization of maleic anhydride and vinyl acetate followed by a simultaneous saponification and hydrolysis step to yield the copolymer. Because these copolymers were polymerized in an aqueous polymerization, some of the vinyl acetate is hydrolyzed prior to the saponification and hydrolysis step. Furthermore, there is no teaching in the Yukagaku article of the partial hydrolysis of only the anhydride portion of the copolymer and not the acetate portion of the copolymer.
U.S. Pat. No. 4,009,110 discloses copolymers containing as polymerized units monomers of maleic anhydride, diketene and vinyl alkyl ether, in a molar ratio of 1:(0.7 to 0.9):(0.1 to 0.3) and their subsequent use in detergent applications. These copolymers are polymerized using a non-aqueous process. Once formed, these copolymers are then hydrolyzed whereby either the maleic anhydride ring or both the maleic anhydride ring and the lactone ring are hydrolyzed.